.PS
ellipseht = .30i
ellipsewid = .60i
boxht = .28i
boxwid = .50i
light = .08
dark = .2
linethick = 1
linewid = .2
lineht = .2
[	A:	ellipse "$D sub 1$"
]
"=" at last [].A.e + .25,0
[	ellipse "$D sub 1$"
] with .w at last [].e + .5,0
.PE
